Please describe the problem:
The 'prefer plain-text' plugin disables the correct handling of meeting invites sent from Outlook -- only the first of the multipart/alternative message is displayed, making it impossible to accept/decline/yada a meeting invite.

Since the 'prefer plain-text' plugin is enabled by default, this means that meeting acceptance for Outlook/Exchange is broken by default.

As the 'prefer plain-text' plugin is listed as 'unsupported demonstration code only', having the plugin enabled by default seems daft.

This is also related to http://bugzilla.gnome.org/show_bug.cgi?id=529397 and http://bugzilla.gnome.org/show_bug.cgi?id=532384

Steps to reproduce:
1. Have a meeting invitation sent from Outlook to a default Evolution configuration
2. Open the meeting invitation
3. Note that no information or acceptance buttons exist.


Actual results:
Only the first part of the multipart/alternative message is shown (including via "view full message", although "view raw message" shows the entire message contents in all parts)

Expected results:
The full meeting information, including the accept/decline buttons should be visible.

Does this happen every time?
Yes.

Other information:
This issue is deeply problematic for anybody using Evolution as an alternative to Outlook or Entourage in an Outlook/Exchange environment.  Since this is such a trivial fix, it's unfortunate that it's persisted since 2.22.0.